(a) Technical Field
The present disclosure relates, in general, to an integrated valve system for a fuel cell stack. More particularly, the present invention relates to a novel integrated valve system for a fuel cell stack, in which an air shut-off valve for suitably preventing the inflow of air when a fuel cell shuts down and a dry gas purge valve for suitably improving cold startability are coaxially coupled to each other so that the air shut-off valve and the dry gas purge valve simultaneously open or close.
(b) Background
The catalyst deterioration of a fuel cell stack occurs in the start-up and shut-down cycles of a fuel cell vehicle.
It has been reported that the catalyst deterioration of each electrode (cathode or anode) in the stack in the start-up and shut-down cycles of a fuel cell is larger than that in idling and loading cycles.
Preferably, in order to easily start up the fuel cell vehicle under conditions below the freezing point, water must be removed from the cathode of the fuel cell stack before the shut-down cycle is performed, to prevent it from freezing. As one method for removing the water, for example, a gas purge method using an air blower has been used. However, discharged water which is purged is re-circulated through a humidifier to the stack, so that water is not perfectly removed.
Another method for removing water has been proposed that preferably uses a dry air purge method for supplying only dry air from the air blower to the fuel cell stack. Preferably, a humidifier bypass valve is suitably installed at the inlet side of the humidifier to bypass wet gas when it tries to enter the cathode.
However, it is difficult to start because of a drop of cell voltage of the fuel cell resulting from the freezing of water remaining in the stack. Conversely, according to the dry air purge method of supplying only dry air, there is no drop of cell voltage resulting from the freezing of water remaining in the stack, so that it is possible to start it.
As such, conventionally, the air shut-off valve is suitably installed at each of the inlet side and outlet side of the cathode so as to prevent air (oxygen), which causes the catalyst to suitably deteriorate during the start process of the fuel cell, from entering the cathode, and the humidifier bypass valve is further installed at the humidifier inlet side to send wet gas entering the cathode to the humidifier. This is problematic in that it has difficulty in securing a valve mounting space, and a valve mounting structure is complicated.
Further, this has a drawback in that several valves must be additionally installed, so that manufacturing cost is considerably increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.